Particulate sensor and method for manufacturing particulate sensor

Abstract

A particulate sensor (10) to be attached to a gas flow pipe EP through which a gas to be measured EG containing particulates S flows. The particulate sensor (10) includes a gas introduction discharge pipe (31); a discharge element (60) including a discharge electrode member (62) maintained at a discharge potential DV and which electrifies particulates contained in the gas under measurement, and a sealed portion (60C) located on a proximal end side GK of an element distal end portion and in which the discharge electrode member is disposed and insulated from the outer surface (60CS) thereof; a surrounding member (38, 39) maintained at a first potential SGND; and an electrically conductive glass seal (37) which establishes electrical communication between the surrounding member and the pipe (31), and is in close contact with the outer surface of the sealed portion of the discharge element to provide gastight sealing.

What is claimed is: 
     
       1. A particulate sensor which is to be attached to a metallic gas flow pipe through which a gas to be measured containing particulates flows and which gas flow pipe is maintained at ground potential, the particulate sensor detecting the particulates contained in the gas to be measured,
 the particulate sensor comprising: 
 a gas introduction discharge pipe into which a gas under measurement, which is a portion of the gas to be measured, is introduced and from which the gas under measurement is then discharged; 
 a discharge element which is formed of insulating ceramic and includes a discharge electrode member maintained at a discharge potential different from the ground potential, the discharge element having 
 an element distal end portion which is located on a distal end side of the discharge element, which element distal end portion is disposed in the gas introduction discharge pipe, and electrifies the particulates contained in the gas under measurement by means of discharge between the discharge electrode member and the gas introduction discharge pipe, and 
 a sealed portion which is located on a proximal end side of the element distal end portion and in which the discharge electrode member is disposed and insulated from an outer surface thereof; 
 a surrounding member which is maintained at a first potential different from both the ground potential and the discharge potential and which surrounds an element proximal end side portion of the discharge element located on the proximal end side with respect to the sealed portion; and 
 an electrically conductive seal which is formed of electrically conductive glass, establishes electrical communication between the surrounding member and the gas introduction discharge pipe, and is in close contact with the outer surface of the sealed portion of the discharge element so as to provide gastight sealing, 
 wherein the electrically conductive glass is obtained by either (a) heating an insulating glass powder and an electrically conductive powder, or (b) heating an electrically conductive glass powder containing a metal-coated glass powder. 
 
     
     
       2. The particulate sensor as claimed in  claim 1 , wherein
 the discharge element includes an element heater wiring line which is connected at one end to the ground potential and which heats the element distal end portion, and a shield electrode layer which is disposed between the element heater wiring line and the discharge electrode member so as to electromagnetically shield the element heater wiring line and the discharge electrode member from each other; and 
 the shield electrode layer electrically communicates with the electrically conductive seal. 
 
     
     
       3. The particulate sensor as claimed in  claim 2 , wherein
 the discharge element has a shield electrode pad which is formed on the outer surface of the sealed portion and electrically communicates with the shield electrode layer; and 
 the shield electrode layer electrically communicates with the electrically conductive seal through the shield electrode pad. 
 
     
     
       4. The particulate sensor as claimed in  claim 2 , wherein
 the shield electrode layer has an extension portion extending to the outer surface of the discharge element; and 
 the shield electrode layer is connected to the electrically conductive seal at the extension portion. 
 
     
     
       5. The particulate sensor as claimed in  claim 1 , wherein
 the surrounding member includes an inner tube formed of metal and having the shape of a tube with a bottom, the inner tube having a closed distal end bottom portion on the distal end side and an insertion hole formed in the distal end bottom portion and through which the discharge element is inserted, the inner tube surrounding the element proximal end side portion of the discharge element from the radially outer side; and 
 the distal end bottom portion of the inner tube contacts the electrically conductive seal from the proximal end side. 
 
     
     
       6. The particulate sensor as claimed in  claim 1 , wherein
 the electrically conductive glass is obtained by heating the insulating glass powder and the electrically conductive powder. 
 
     
     
       7. The particulate sensor as claimed in  claim 1 , wherein
 the electrically conductive glass is obtained by heating the electrically conductive glass powder containing the metal-coated glass powder. 
 
     
     
       8. The particulate sensor as claimed in  claim 1 , wherein
 the electrically conductive seal directly contacts the sealed portion of the discharge element. 
 
     
     
       9. A particulate sensor which is to be attached to a metallic gas flow pipe through which a gas to be measured containing particulates flows and which gas flow pipe is maintained at ground potential, the particulate sensor detecting the particulates contained in the gas to be measured,
 the particulate sensor comprising: 
 a gas introduction discharge pipe into which a gas under measurement, which is a portion of the gas to be measured, is introduced and from which the gas under measurement is then discharged; 
 a discharge element which is formed of insulating ceramic and includes a discharge electrode member maintained at a discharge potential different from the ground potential, the discharge element having 
 an element distal end portion which is located on a distal end side of the discharge element, which element distal end portion is disposed in the gas introduction discharge pipe, and electrifies the particulates contained in the gas under measurement by means of discharge between the discharge electrode member and the gas introduction discharge pipe, and 
 a sealed portion which is located on a proximal end side of the element distal end portion and in which the discharge electrode member is disposed and insulated from an outer surface thereof; 
 a surrounding member which is maintained at a first potential different from both the ground potential and the discharge potential and which surrounds an element proximal end side portion of the discharge element located on the proximal end side with respect to the sealed portion; and 
 an electrically conductive seal which is formed of electrically conductive glass, establishes electrical communication between the surrounding member and the gas introduction discharge pipe, and is in close contact with the outer surface of the sealed portion of the discharge element so as to provide gastight sealing; 
 a tubular insulating spacer which is formed of insulating ceramic and which is disposed radially outward of a distal end side portion of the surrounding member on the distal end side, the electrically conductive seal, and a pipe proximal end side portion which is a portion of the gas introduction discharge pipe on the proximal end side; 
 the electrically conductive seal is in gastight close contact with an inner circumferential surface of the insulating spacer; and 
 the distal end side portion of the surrounding member and the pipe proximal end side portion of the gas introduction discharge pipe are fixed to the insulating spacer through the electrically conductive seal. 
 
     
     
       10. The particulate sensor as claimed in  claim 9 , wherein
 the insulating spacer has a stepped spacer ledge portion projecting radially inward; 
 the pipe proximal end side portion of the gas introduction discharge pipe has a stepped pipe shoulder portion whose diameter on the distal end side is smaller than that on the proximal end side and which engages the spacer ledge portion, and a pipe proximal end portion which is located on the proximal end side of the pipe shoulder portion and has an end edge on the proximal end side; and 
 the electrically conductive seal is in contact with the pipe proximal end portion. 
 
     
     
       11. The particulate sensor as claimed in  claim 10 , further comprising an element holder which is formed of insulating ceramic and which has, on its outer circumferential surface, a stepped holder shoulder portion whose diameter on the distal end side is smaller than that on the proximal end side and which engages the pipe shoulder portion of the gas introduction discharge pipe, and an insertion hole through which an element insertion portion of the discharge element between the element distal end portion and the sealed portion is inserted, wherein the element holder holds the discharge element at the through hole, and butts against the electrically conductive seal from the distal end side. 
     
     
       12. A method of manufacturing a particulate sensor which is to be attached to a metallic gas flow pipe through which a gas to be measured containing particulates flows and which gas flow pipe is maintained at ground potential, the particulate sensor detecting the particulates contained in the gas to be measured, the particulate sensor comprising:
 a gas introduction discharge pipe into which a gas under measurement, which is a portion of the gas to be measured, is introduced, and from which the gas under measurement is then discharged; 
 a discharge element which is formed of insulating ceramic and includes a discharge electrode member maintained at a discharge potential different from the ground potential, the discharge element having 
 an element distal end portion which is located on a distal end side of the discharge element, is disposed in the gas introduction discharge pipe, and electrifies the particulates contained in the gas under measurement by means of discharge between the discharge electrode member and the gas introduction discharge pipe, and 
 a sealed portion which is located on a proximal end side of the element distal end portion and in which the discharge electrode member is disposed and insulated from an outer surface thereof; 
 a surrounding member which is maintained at a first potential different from both the ground potential and the discharge potential and which surrounds an element proximal end side portion of the discharge element located on the proximal end side with respect to the sealed portion; and 
 an electrically conductive seal which is formed of electrically conductive glass, establishes electrical communication between the surrounding member and the gas introduction discharge pipe, and is in close contact with the outer surface of the sealed portion of the discharge element so as to provide gastight sealing, 
 wherein the method comprises a seal forming step of bringing softened electrically conductive glass into close contact with outer surfaces of the surrounding member, the gas introduction discharge pipe, and the sealed portion of the discharge element to thereby form the electrically conductive seal, and 
 the electrically conductive glass is obtained by either (a) heating an insulating glass powder and an electrically conductive powder, or (b) heating an electrically conductive glass powder containing a metal-coated glass powder. 
 
     
     
       13. The method as claimed in  claim 12 , wherein
 the electrically conductive glass is obtained by heating the insulating glass powder and the electrically conductive powder. 
 
     
     
       14. The method as claimed in  claim 12 , wherein
 the electrically conductive glass is obtained by heating the electrically conductive glass powder containing the metal-coated glass powder. 
 
     
     
       15. The method as claimed in  claim 12 , wherein
 the electrically conductive seal directly contacts the sealed portion of the discharge element.